An engine crankshaft converts reciprocating linear movement of a piston into rotational movement about a longitudinal axis to provide torque to propel a vehicle, such as but not limited to a train, a boat, a plane, a truck, or an automobile.
The crankshaft includes at least one crankpin that is offset from the longitudinal axis, to which a reciprocating piston is attached via a connecting rod. Force applied from the piston to the crankshaft through the offset connection therebetween generates torque in the crankshaft, which rotates the crankshaft about the longitudinal axis. The crankshaft further includes at least one main bearing journal disposed concentrically about the longitudinal axis. The crankshaft is secured to an engine block at the main bearing journals. A bearing is disposed about the main bearing journal, between the crankshaft and the engine block.
In order to reduce weight of the crankshaft, the crankpins and main bearing journals may have hollow portions. The maximum volume of the hollow portions, and thus the weight reduction of the crankshaft, is limited by the stresses that must be borne by the crankshaft during engine operation. Stated differently, the crankshaft must have a sufficient thickness in order for the crankshaft to bear the stresses.